Method of preparing improved wood preservative from coal tar creosote



`servative by any standard procedure.

United States Patent O 3,046,217 METHOD F- PREPARING IMPROVED WOOD PRE- SERVATIVE'FRM COAL TAR CREGSOTE William F..Hafner, Monroeville, CharlesW. Leach, Trafford, and ThomasW. Smeal, Jeannette, Pa., assignors to United States Steel Corporation,` a corporation of New Jersey Filed May 15, 1959, Ser. No. 813,515 2` Claims. (Cl. 208-2) paring an improved Wood preservative by oxidizing impurities normally present in coal tar creosote, separating oxidized impurities by distillation, and ltering crystalline materials from the distillate, leaving a light-colored preservative of mild odor.

A further, object is to provide an improved method of preservingA wood in which a Wood body is impregnated with a preservative prepared in the foregoing manner.

`Other objects are to provide an improved preservative from coal tar creosote which is light-colored and of.

only mild odor, and4 an improved wood product resulting fromimpregnation therewith.

In the drawing:

The single FIGURE is a schematic owsheet showing the steps of our method.

We prepare our improved Wood preservative from conventional coal tar creosote which has a minimum boiling point of about 230 C. and possesses the usual murky brown color and strong odor. First We heat such creosote to about 100-150 C. While the creosote is` maintained at this temperature, We introduce streams of air thereto at4 a. rate of about "60 to 100 standard cubic feet per minute per ton of creosote for at least one hour. Some of the more easily oxidized saturated cyclic compounds in the creosote oxidize and form stable oxidation products. After the air-blowing step, the color of the creosote changes to a dull black. As a separate step, We then distill the air-blown creosote under a vacuum, preferably equivalent to about 60 mm. of mercury, to an end temperature equivalent to an end temperature of about 395-410 C. at atmospheric pressure. The oxidized impurities remain as residue, While the purified creosote is the distillate. We consider it necessary to perform the air-blowing and vacuum distillation steps separately, since performing them simultaneously would not permit sufficient contact time with the air. Next We cool the distillate to a maximum temperature of about C., thereby forming crystals rich in anthracenephenanthrenecarbazol. Finally we remove these crystals by a ltration or equivalent step, recovering our completed preservative as ltrate. The drawing shows the foregoing steps only schematically, since the individual pieces of apparatus are conventional.

The resulting preservative is only lightly colored, and if desired it can be dyed various shades. The odor is mild. A Wood body can be impregnated with our pre- The resulting wood product is durable and has a light pleasing color and mild scent. Crystals recovered in the filtration step also are a valuable by-product.

3,046,217 Patented July 24, 1962 ice 2. Example` Ivv As a specific exampleto illustrate our, methd, We se; lectedf as starting material a sample-.ofcoal tar CLGOSOQ having the following zphysical characteristics.:

Specific gravity 32E/15.5 C 1,1014-A Percent of crystals at 38 C 1.1.4, Creosoter.s distillationpattern (AWPA A1-57') to- 210 C. percent 0.0 235 C dQ 0,33 2.70, C do, g 8.5 315.o C dg, 40.9 355. C do 71.0 4.00.o C cl 90.0 Residue. do 9.4 Loss do 0.6 First drop C-- 233` ff American.. WQ-od-Breservels ASQCltim Manuel 0f Recommended Practice, Subject Designation' A1-57.

This sample, was air-blown (air at roorn temperature)` for 1 1/2 hours,` with; an air flow rate equivalent to` 80, s.c.f.m; per ton of creosote. During this operation, the. temperature of, the creosote-rose` fromv 135.u C. to C; The color of the creosote after being ain-blown, was a dull black (compared, to the original murkyebrown colon), indicating the` formation ofA objectionable corrp. pounds.

A sample ot this.` air-blown creosote was then redis-` tilledfasfollows;

Disillate, percent Distillation temp., C., to of original weight vResidue percent i122 Loss do 0.4. First drop C-- 2,51

The residue above 400 C. from this distillation was discarded. The 235 to 400 C. fraction was then vacuum-ltered through a ZOO-mesh sieve at 38 C., removing 15.0 percent by weight of the original creosote in the form of crystals. v

The creosote produced by these operations was a clear oil with a light-yellow color and having little of the characteristic odor of creosote. It represented 72.8 percent by weight of the starting material, was crystal-free at 38 C., and had the following distillation pattern (AWPA A1-57).

Distillate, percent Distillation temp., C., toof original weight Residue percent-- 4.6 Loss do 0.5 First drop C-- 247 Soil-block bioassay and permanence studies indicated that this creosote had wood-preserving properties as good as, or slightly better than, AWPA grade 1 creosotes.

Example 2 Distillation temp., C., toof original weight Residue percent 19.0 Loss do 0.4 First drop C 261 The residue above 400 C. from this distillation was discarded. The 235 to 400 C. fraction was then vacuumiiltered through a 200-mesh sieve at 38 C., removing 13.1 percent by weight of the original material in the form of crystals.

The creosote produced by these operations was a clear oil with a light-yellow color and having little of the characteristic odor of creosote. It represented 67.9 percent by weight of the starting material, was crystal free at 38 C., and had the following distillation pattern (AWPA A1-57):

Distillate, percent Distillation temp., C., to of original weight Residue percent 6.2 Loss do 0.9 First drop C 255 Soil-block bioassay and permanence studies indicated that this creosote had wood-preserving properties as good as, or slightly better than, AWPA grade 1 creosotes.

From the foregoing description and examples it is seen that our invention affords a simple method of preparing an improved wood preservative from coal tar creosote, but eliminating objectionable color and odor. Our preservative retains all the desirable characteristics of conventional creosote, and the absence of crystalline substances permits easier transfer through pipes and pumps, lessens the heat required to maintain fluidity, and facilitates the impregnation process.

While we have shown and described certain preferred ways of practicing our invention, it is apparent that other modifications may arise. Therefore, we do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

We claim:

1. A method of preparing a reiined creosote from coal tar creosote which has a minimum boiling point of about 230 C. comprising heating said coal tar creosote to about 100-150 C., introducing an air stream to the heated coal tar creosote at a rate of about 60 to 100 standard cubic feet per minute per t0n of coal tar creosote for at least one hour and thus oxidizing unsaturated cyclic compounds present in the coal tar creosote and forming stable oxidation products, as a separate step distilling the coal tar creosote under vacuum to an end temperature corresponding to an end temperature of about 395-410u C. at atmospheric pressure and thus separating a creosote product as distillate and said oxidation products as residue, cooling said distillate to a maximum temperature of about 40 C., and filtering said cooled distillate to remove crystals rich in anthracene-phenenathrene-carbazol, thus recovering a rened creosote having a light color and mild odor.

2. A refined creosote prepared according to the method defined in claim 1.

References Cited in the tile of this patent UNITED STATES PATENTS 1,037,832 Newton Sept. 3, 1912 2,066,583 Shipley Ian. 5, 1937 2,095,190 Heuscher Oct. 5, 1937 2,246,973 Camilli June 24, 1941 2,655,454 Farber et al Oct. 13, 1953 2,864,846 Gragson Dec. 16, 1958 

1. A METHOD OF PREPARING A REFINED CRESOTE FROM COAL TAR CREOSOTE WHICH HAS A MINIUMUM BOILING POINT OF ABOUT 230*C. COMPRISING HEATING SAID COAL TAR CRESOTE TO ABOUT 100-150*C., INTRODUCING AN AIR STREAM TO THE HEATED COAL TAR CREOSOTE AT A RATE OF ABOUT 60 TO 100 STANDARD CUBIC FEET PER MINUTE PER TON OF COAL TAR CREOSOTE FOR AT LEAST ONE HOUR AND THUS OXIDIZING UNSATURATED CYCLIC COMPOUNDS PRESENT IN THE COAL TAR CREOSOTE AND FORMING STABLE OXIDATION PRODUCTS, AS A SEPARATE STEO DISTILLING THE COAL TARCREOSOTE UNDER VACUUM TO AN END TEMPERATURE CORRESPONDING TO AN END TEMPERATURE OF ABOUT 395-410*C. AT ATMOSPHERIC PRESSURE AND THUS SEPARATING A CREOSOTE PRODUCT AS DISTILLATE AND SAID OXIDATION PRODUCCTS AS RESIDUE, COOLING SAID DISTILLATE TO A MAXIMUM TEMPERATURE OF ABOUT 10*C., 